Recent advancements in solar cell technology have helped overcome many barriers to producing highly efficient and economically viable photovoltaic (PV) modules. Traditionally, crystalline silicon (c-Si) based solar cells have relied on the use of silver (Ag) grids (e.g. fingers and busbars) for collecting current. Ag grids are formed by printing Ag paste onto wafers and firing the past at temperatures between 700-800° C.
Newer solar cells use amorphous Si (a-Si) to form a heterojunction with a c-Si layer or provide for surface passivation. However, a-Si cannot be processed at temperatures exceeding 200° C., and therefore not compatible with traditional Ag paste. One approach to this issue was the use of low temperature Ag paste to form the conductive grid. However, low temperature Ag paste is highly resistive compared to traditional paste and therefore required a comparatively thick layer. This required using a layering technique in which several layers of low temperature paste were successively applied. The cost and complexity of that process was ultimately prohibitive.
A different approach to this issue was to not use Ag paste at all, but instead apply a layer of copper, which can be etched by photolithography to form the grid. But using copper presented its own issues, as copper does not adhere well to silicon using electroplating techniques. Innovators of the industry, such as Silevo Inc., pioneered processes in which a thin seed layer of copper is first applied to the a-Si by physical vapor deposition. This seed layer has excellent adhesion properties, and forms the basis for a thick layer of copper deposited by electroplating. Details of such a process is disclosed at Pub. No. US20130125974A1, which is incorporated by reference herein.
Clearly, solar technology has made great strides in recent years through breakthroughs for increasing efficiency of PV modules. Such improvements are making solar energy a more viable energy source. In spite of these technological breakthroughs in efficiency, cost per watt is perhaps the most determinative factor when deciding to implement solar power. Thus, any aspect of the PV module manufacturing process that can increase throughput, and hence lower cost, has great importance for the viability of solar energy.
Electroplating copper is normally a simple procedure, but in spite of the seed layer, electroplating of silicon solar cells can still be a manually intensive process. This is because each solar cell requires manual placement of several small plating electrodes onto sections of the solar cell to form the electroplated layer. Each electrode must be individually placed and aligned. Because several electrodes required per solar cell, this can make for a very time consuming process, which can be troubled by breakages due to the intensive handling required. Accordingly, improving this process and reducing handling is important for improving throughput of PV module production.